Youtube is now making some high resolution videos available. If you find a video you'd like to watch, you can add the following text to the webpage address, "&fmt=6" (without the quotes) to get a better picture. For the higher quality version you might need to wait a bit longer than for the normal version, because the size of the file is bigger, so it takes more time to download.

For example you can take a look at these two videos and compare the difference:-

http://www.youtube.com/watch?v=QAE2-FQHkok
http://www.youtube.com/watch?v=QAE2-FQHkok&fmt=6

For the more technically oriented, there's a greasemonkey script available to automatically show the high-res video if available.

Also if you add "&fmt=18" instead of &fmt=6 you'll get the video in mp4 format instead of the usual .flv format usually used by youtube.

Via Hackzine